1. Field of the Invention
The present invention relates to a method for adjusting an optical axis of an imaging optical system for use in an electronic still camera, a video camera and a silver halide camera, and an lens system.
2. Description of Related Art
Among cameras which are propagated generally there are so-called digital cameras which are cameras in which a subject image captured by an imaging optical system is sensed by an image sensing unit such as a CCD image sensor. In recent years, miniaturized or streamlined digital cameras constitute a main stream of the design of such digital cameras. As imaging optical systems for use in these digital cameras, there is raised a so-called refractive optical system in which subject light taken to follow a first optical axis is bent, by the use of a prism and a mirror, toward a second optical axis which intersects the first optical axis at right angles, so that the subject light bent forms an image or is focused on a focal plane of a CCD image sensor disposed on the second optical axis. Among these refractive optical systems, there is provided a refractive optical system in which a lens group which contributes to zooming is moved by a drive source to change the zooming magnification.
Since optical components which constitute a refractive optical system like this are incorporated in a camera main body as a single unit, it is general practice that these optical components are incorporated in the same lens barrel. In the case of the refractive optical system in which the lens group which makes up the optical components is moved so as to change the zooming magnification, however, since assembling and adjusting in association with assembly of the lens group which moves when changing the zooming magnification is difficult, the optical performance of the whole refractive optical system is difficult to be maintained with high accuracy. In recent years, digital cameras provided with refractive optical systems having high zooming magnifications tend to constitute the main stream of trend of digital cameras, and as the zooming magnification is increased, maintaining the optical performance of the refractive optical system with high accuracy gets more difficult.
As a method for increasing the optical performance of the refractive optical system, there is proposed a method in which a lens barrel is made up of, for example, a cover in which a prism is incorporated and an outer barrel in which the other optical components are incorporated, and a shaft portion which protrudes from a total reflection surface of the prism is passed through a passage hole provided in the cover, so that the angle of a light incident surface of the prism is adjusted by operating rotationally the shaft portion which protrudes from an external part of the cover, so as to increase the accuracy of the optical performance of the whole refractive optical system (JP-A-2005-148663 and the like).
However, adjusting the angle of the light incident surface of the prism is premised on the fact that the direction of an optical axis of light that emerges from an light emerging surface of the prism coincides with the direction of an optical axis of the optical components that are incorporated in the outer frame, and in case the assembling accuracy of the outer barrel to the cover is low, the assembling accuracy of the cover to the prism is low or the assembling accuracy of the optical components which are assembled on to the outer barrel is low, the accuracy of the optical performance of the whole refractive optical system cannot be increased only by adjusting the angle of the light incident surface of the prism as described above.